However the mic doesn't seem to pick up any sound when Its plugged in and I'm not sure if this is an issue with the headset or if maybe these headphones mic is not compatible with the S4 Mini? Because I've had these headphones for a while but never really used the mic on it for calls and then I got the S4 Mini and wanted to use the Mic on it but realised that it doesn't work but sometimes when I'm on skype i'd have to plug in plug out and mess around with the headphones and the mic would randomly work?

You can probably find a handsfree with decent earphones in a dollar store for a buck or two. Cheaper and faster (especially if Amazon sends your package to the wrong post office like they just did to me - it's been sitting there for 4 days and all Amazon can tell me is "wait another 4 days". If Bezos were dead he'd be spinning in his grave.).